Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Field effect transistor
Patent
1998-06-18
2000-02-22
Ngo, Ngan V.
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Field effect transistor
257192, H01L 310328, H01L 310336, H01L 31072, H01L 31109
Patent
active
060283289
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Pseudomorphic HEMTs (high electron mobility transistors)--abbreviated PHEMT in the following--grown on a GaAs substrate are field effect transistors with a braced channel layer, in which the doping atoms that provide the charge carriers required for the charge transport from the source to the drain are wholly or partially spatially separated from the channel in which the charge transport takes place. The construction of the semiconductor layer structure required therefor is grown epitaxially. The channel, which standardly consists for example of In.sub.y Ga.sub.1-y As, thereby has the following characteristics:
1. The lattice constant of the semiconductor crystal in the channel is (dependent on the In content y) different from the lattice constants of the surrounding semiconductor materials and of the substrate (thus the designation "pseudomorphic"). Thus, the thickness of the channel is limited if displacements, which can occur due to the insufficient adaptation of the lattice constants and which have an adverse effect on the charge carrier transport characteristics, are to be avoided.
2. The transport characteristics of the charge carriers are better in the channel than in the adjacent semiconductor layers, which likewise depends on the In portion y.
3. The energy band gap is smaller in the channel than in the adjacent layers. For this reason, the charge carriers are transferred from the doped layers adjacent to the channel into the channel, and are effectively enclosed there, i.e. in the region with the best transport characteristics. However, the energy band gap of the channel cannot be reduced arbitrarily, because very small band gaps can be achieved only with In portions y that cause sharp deviations of the lattice constants from that of the substrate or, respectively, of the remaining semiconductor layers, and, consequently, enable only very small thicknesses of the channel.
In the design of epitaxial layers for PHEMTs, a compromise must thus be found. Contents y of In that were selected with respect to a minimum band gap allow only channel thicknesses small enough that the number of charge carriers enclosed in the channel is very small, and their transport characteristics are strongly adversely influenced by the channel boundary surfaces lying close to one another. Channels that have been optimized on one side to a large thickness have band gaps that differ only slightly from those of the adjacent layers, so that the charge carriers are no longer transferred effectively from the doped layers into this channel, and are enclosed there only defectively. Moreover, in these channels the transport characteristics are only slightly superior to those of the adjacent layers.
PHEMTs on the basis of GaAs have been used up to now in two basic forms, known as single heterojunction PHEMT (SH-PHEMT) and double heterojunction PHEMT (DH-PHEMT). Both basic forms have a channel in common, which, given In portions y of 0.2 to 0.25, is typically 10 nm to 12 nm thick.
In the SH-PHEMT, the In.sub.y Ga.sub.1-y As channel is bounded below by a GaAs layer, and above by a semiconductor material that comprises a greater difference of the energy band gap to InGaAs than GaAs, standardly by means of Al.sub.x Ga.sub.1-x As, more rarely by means of In.sub.z Ga.sub.1-z P. In the SH-PHEMT, doping atoms are located only in the layer above the channel, i.e. between the channel and the surface of the component or, respectively, between the channel and the gate contact, but not in the GaAs under the channel. This means that the lower boundary of the conduction band runs in the direction perpendicular to the boundary surface between the semiconductor material and the gate contact, as shown in FIGS. 2 and 3. Given gate voltages close to the cutoff voltage of the transistor, the conduction band edge runs in the channel almost parallel to the Fermi energy, by which means the location probability of the charge carriers is greatest approximately in the center of the channel (see FIG. 2). Given more positive gate v
REFERENCES:
patent: 5449928 (1995-09-01), Matsugatani et al.
patent: 5453631 (1995-09-01), Onda et al.
patent: 5751029 (1998-05-01), Matsushita et al.
patent: 5844260 (1998-12-01), Ohori
patent: 5945693 (1999-08-01), Shzhki et al.
IEEE Electron Device Letters, vol. 15, No. 11, Nov. 1994, M. Wojtowicz et al, 0.10 .mu.m graded InGaAs Channel InP HEMT with 305 GHz f.sub.T and 340 GHz f.sub.max, 477-479.
Proceedings of the International Conference on Indium Phosphide and Related Materials, Santa Barbara, Mar. 1994, Conf. No. 6, K. B. Chough et al, High-Performance InP-based HEMT's with a Graded Pseudomorphic Channel, pp. 427-430.
Applied Physics Letters, vol. 61, No. 16, Oct. 1992, Tae-Kyung Yoo et al, Double modulation-doped AlGaAs/InGaAs heterostructure with a graded composition in the quantum well, pp. 1942-1944.
Grave Thomas
Riechert Henning
Ngo Ngan V.
Siemens Aktiengesellschaft
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